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Glycolipids

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Glycolipids comprise another major class of glycans. These molecules are abundant components of the cellular membrane and consist of a lipid moiety attached to monosaccharide or polysaccharide chains that extend into the extracellular space.

  • Classes of glycolipids include glyceroglycolipids, lipopolysaccharides, glycosphingolipids, and glycosylphosphatidylinositols (1).
  • Glycolipids have varied functions (2,3) some of which include:
    • Eliciting host immune responses to bacterial infections
    • Modulating cell-cell communication
    • Ensuring proper myelination of axons
  • One class glycosylphosphatidylinositol anchors (GPI) attach certain proteins to the surface of eukaryotic cells.
    • GPI anchored proteins are involved in a variety of cellular processes including cell adhesion and signal transduction.
    • GPI anchored proteins also typically possess N- and/or O-linked glycans (Fig. 1).
    • GPI anchors appear to be involved in the trafficking and surface localization of a given protein, for instance there seems to be a higher abundance of GPI-anchored proteins in lipid rafts (4).

Figure 1: Schematic representation of the main events in the synthesis of GPI-anchored proteins. Proteins (often glycoproteins) acquire a GPI anchor in the ER, a signal sequence is cleaved (at a consensus omega residue) and the GPI anchor is attached via a terminal ethanolamine phosphate to the C-termini of the acceptor protein. The glycolipid moiety can be later modified in the Golgi. The mature glycoprotein is finally localized to the plasma membrane.

References:

  1. Bastow ER, et al. (2008) Cell Mol Life Sci. 65(3):395-413. PMID: 17965830
  2. Zajonc DM, Kronenberg M. (2009) Immunol Rev. 230(1):188-200. PMID: 19594637
  3. Stoffel W, Bosio A. (1997) Curr Opin Neurobiol. 7(5):654-61. PMID: 9384539
  4. Paulick MG, Bertozzi CR. (2008) Biochemistry. 47(27):6991-7000. PMID: 18557633

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